The 17-electron radical CpCr(CO)(2)(IMe)(center dot) (IMe = 1,3-dimethylimidazol-2-ylidene) was synthesized by the reaction of IMe with [CpCr(CO)(3)](2), and characterized by single crystal X-ray diffraction and by electron paramagnetic resonance (EPR), IR, and variable temperature H-1 NMR spectroscopy. The metal-centered radical is monomeric under all conditions and exhibits Curie paramagnetic behavior in solution. An electrochemically reversible reduction to 18-electron CpCr(CO)(2)(IMe)(-) takes place at E-1/2 = 1.89(1) V vs Cp2Fe+./0 in MeCN, and was accomplished chemically with KC8 in tetrahydrofuran (THF). The salts K+(18-crown-6)[CpCr(CO)(2)( IMe)](-).1/ 2 T H F and K+ [CpCr-(CO)(2)(IMe)](-.3/4) THF were crystallographically characterized. Monomeric ion pairs are found in the former, whereas the latter has a polymeric structure because of a network of K center dot center dot center dot O-(CO) interactions. Protonation of K+(18-crown-6)[CpCr(CO)(2)(IMe)](-1/2) THF gives the hydride CpCr(CO)(2)(IMe)H, which could not be isolated, but was characterized in solution; a pK(a) of 27.2(4) was determined in MeCN. A thermochemical analysis provides the Cr-H bond dissociation free energy (BDFE) for CpCr(CO)(2)(IMe)H in MeCN solution as 47.3(6) kcal mori. This value is exceptionally low for a transition metal hydride, and implies that the reaction 2[Cr-H] -> 2[Cr] + H-2 is exergonic (triangle G = -9.0(8) kcal mol(-1)). This analysis explains the experimental observation that generated solutions of the hydride produce CpCr(CO)(2)(IMe)(center dot) (typically on the time scale of days). By contrast, CpCr(CO)(2)(PCy3)H has a higher Cr-H BDFE (52.9(4) kcal mol(-1)), is more stable with respect to H2 loss, and is isolable.